There has been known that such an exhaust purification system includes an injection nozzle that adds urea water into an exhaust pipe, and a selective reduction catalyst (referred to as SCR catalyst hereinafter) that takes ammonia generated from the urea water by hydrolysis with exhaust heat as a reducing agent and reduces and purifies nitrogen compounds (referred to as NOx hereinafter) contained in exhaust gas.
When distribution of the reducing agent supplied to the SCR catalyst is uneven, the ammonia becomes excessive in a region where a supply amount is large while the NOx cannot be sufficiently reduced and purified in a region where a supply amount is insufficient. Therefore, in order to improve reduction efficiency, it is necessary to mix and diffuse the reducing agent in the exhaust gas so as to evenly distribute the reducing agent in the SCR catalyst. For example, there is disclosed in PTL 1 a technology in which a mixer plate that includes a plurality of fins is provided between a reducing agent injection nozzle and an SCR catalyst so that a reducing agent can be efficiently mixed and diffused in exhaust gas.